Protocol for Structure Determination of Unknowns by EI Mass Spectrometry. V. Diagnostic Ions in the Mass Spectra of Steroids

Electron ionization (EI) induced decomposition pathways are determined for various steroids representing skeletons of estrane, androstane, pregnane, cholane, cholestane, stigmastane and more. Diagnostic ions are identified and recommended for decoding selected structural elements to reconstruct the structure of an unknown. The striking dependencies of the sites of charge localization and bond fissions on the number and the location of hydroxyl, carbonyl, carboxyl, and amine functionalities in the steroid backbone are highlighted to assist in a reliable structure elucidation of unknowns. The controlling status of stereochemistry in EI-induced decomposition of steroids is considered. The potential and limitations of EI mass spectrometry in the structure determination of steroids are emphasized.